1) Field of the Invention
The field of the present invention relates to method and apparatus for optically reading information in multiple formats, and more particularly to a multi-function optical reader for reading bar codes, optical marks and other data in various formats.
2) Background
A variety of devices and techniques for optically reading marks, characters, symbols or other information are currently known. Most such optical reading devices generally have an optical interface for receiving information and a processor for conditioning, processing and/or interpreting the received information, according to the particular type of data (i.e., mark, character, symbol, etc.) to be detected.
Optical mark readers are devices which are used for reading graphical marks on paper or other documents. Typically with optical mark readers, the relative locations of the marks or punchouts on a page indicate data, such as letters, digits, codes, or other such information. The marks may be made automatically by machine (e.g., a printer operating under computer control), or manually using a writing implement. Often the marks are made on a printed xe2x80x9cformxe2x80x9d document which has predefined boxes or other physical areas having a specific meaning attached to them. Examples of such printed form documents include standard form test sheets, voting ballots, and lottery tickets.
An optical mark reader detects the marks on a paper by measuring the amount of light reflected and/or refracted by the paper at specific locations. A white paper background reflects more light than a darker mark or void; thus an optical mark reader can detect a mark when the amount of light reflected and/or refracted from the paper is sufficiently low, and otherwise detects the absence of a mark.
As an example, in the gaming industry optical mark readers are known in which employ a card reader having an array of light-emitting diode (LED) emitter-detector pairs. A card (e.g., a lottery ticket) is manually inserted into a slot of the card reader, which then uses a mechanized operation to pull the card through at high speed. The LED pairs are located at discrete positions in an array spanning the width of the card. As the card is pulled through, the LED pairs are used to read it line by line. Where a sufficiently low level of light is observed by the detector of an LED emitter-detector pair, a mark is assumed to be present. The card reader stores the data or information signified by the mark for subsequent processing. After the card is pulled through, the mark information on it will be entirely read. This reading process for a single card can take approximately one-half of a second.
Another type of optical reading is performed by bar code scanners and similar imaging devices. Flying spot laser scanners have been used to illuminate a target and detect the reflected and/or refracted light on a photodetector. A relatively large amplitude of the photodetector signal indicates a high level of reflected and/or refracted light and, therefore, white spaces of the bar code, while a relatively small amplitude of the photodetector signal indicates a low level of reflected and/or refracted light and, therefore, dark bars of the bar code. The widths of the bars and spaces are measured by signal processing circuitry, and a decoder then determines whether the measured data indicates the presence of a valid bar code based on, for example, the number of bars and spaces, their relative widths and a parity check. Alternatively, a CCD imager can be used in place of a flying spot scanner, and such a CCD imager can be a single line CCD array or else a two-dimensional CCD array. Various techniques for reading and processing bar code and other types of signals are described in, for example, U.S Pat. Nos. 4,000,397, 5,463,211 and 5,446,271, each of which is assigned to the assignee of the present invention, and each of which is hereby incorporated by reference as if set forth fully herein.
Another type of optical reading is performed by optical character recognition (OCR) systems. In these systems, an optical detector captures a single line of data, isolates characters based upon relative contrast (i.e., low reflectance levels), and matches templates of alphanumeric characters to each isolated character in the line of data. An OCR system may repeat this process for each line of data read, and can thereby read and interpret the text on an entire document.
In some applications, it may be desired to have the ability to read data in different formats using the same device and/or machinery. Data may be presented in different formats on the same page or, if an object, on the same surface. For example, a single sheet of paper may contain both characters and bar codes that contain information needing to be read. Various types of xe2x80x9chybridxe2x80x9d readers have been proposed to read data in different formats without using separate devices or machinery. Examples of these are illustrated by U.S. Patent Nos. 4,402,088, 4,877,948, and 5,452,379, each of which is hereby incorporated by reference as if set forth fully herein.
One difficulty with attempting to integrate capabilities of reading multiple data formats in a single device is that each format has its own peculiar requirements for initial optical input and signal conditioning, as well as detection algorithms. As a consequence, circuitry used for one type of data detection would not likely be suitable for detecting data in a different format. In addition, the speed at which the data input occurs is dependent upon the data format. For example, bar code data is generally more concentrated than optical mark data, and needs to be read at a slower rate. However, if a device is constructed such that all data is read at the slowest rate necessary, than overall performance would suffer.
As an additional obstacle, a device for reading multiple data formats would generally need to recognize all possible formats simultaneously, absent some means for assisting with the data recognition process.
The present inventors have therefore determined that it would be advantageous to provide a multiple-function optical reader capable of reading data in a variety of different formats. It would further be advantageous to provide an integrated device capable of reading both bar code or other symbol information and optical marks. It would further be advantageous to provide such a device with additional data reading capability, including the ability to optically read characters or other information. It would further be advantageous to provide any of the above devices having signal conditioning circuitry capable of properly conditioning the variety of possible expected data input formats, and which is compact, relatively easy to integrate, yet not prohibitively expensive to manufacture.
The present invention provides in one aspect an optical reader capable of reading information in multiple formats, such as a bar code format and an OMR (Optical Mark Recognition) format.
In a preferred embodiment of the invention, an optical reader comprises a photosensitive sensor (such as a CCD linear sensor) having an output signal that is processed by multiple signal processing channels, such as a bar code channel and an OMR channel. Outputs from the multiple signal processing channels are provided to a feature measuring circuit, which identifies the relative locations of features of the target to be read, such as widths of light and dark bar code elements or OMR features. The feature measurement data may be transferred to a decoder or other processor for decoding and processing. The decoder may either reside in the same general physical location as the other optical reader circuitry, or may be located external to the optical reader.
In a preferred embodiment of the invention, a FIFO buffer is provided to facilitate transfer of feature measurement data from the feature measurement circuit to the decoder and/or processor. The feature measurement circuit may write to the FIFO buffer simultaneously with the decoder reading out from the FIFO buffer.
In another embodiment of the invention, the exposure time of the photosensitive sensor is controlled dynamically to provide a rapid scanning rate while preventing saturation of the sensor. In an exemplary embodiment employing this technique, a CCD linear sensor is utilized, and its scanning rate is varied from a relatively lower scanning rate (e.g., 250 scans/second) when in a bar code scanning mode to a relatively higher scanning rate (e.g., 1000 scans/second) when in an OMR scanning mode. Additionally, the CCD video output signal may be monitored and, when it is of an amplitude indicating possible saturation, the scanning rate may be increased or else may be rotated among it different rates. Preferably, the read-out rate from the CCD linear sensor is maintained constant even when the scanning rate is increased, so as to maintain the CCD video output signal within the optimal range of the signal processing circuitry.
In another embodiment of the invention, reading may be accomplished by an optical reader in multiple depth of field zones. In a particular embodiment in accordance with this aspect of the invention, an optical reader is capable of reading the front and back of a document (e.g., lottery ticket) inserted into the apparatus, with the front view and the back view of the document providing two different depth of field zones. A third depth of field zone is provided by allowing the optical reader to image targets along the optical scan path but external to the housing of the apparatus.
In another embodiment of the invention, the scanning mode of the optical reader is selected by a special code (e.g., a specialized bar code or symbol, referred to as a xe2x80x9ccontrol symbolxe2x80x9d or sometimes as a xe2x80x9cjob control bar codexe2x80x9d) affixed to the target to be read. The optical reader first looks for the special code and, when detected, configures itself in the proper mode (i.e., bar code scanning mode or OMR scanning mode) for the anticipated data from the target. The special code or control symbol can also be used to identify the data format used in specific regions of the target, so that the optical reader can dynamically change modes during reading of a single target based upon the information from the special code or control symbol.
In yet another embodiment of the invention, an optical reader provides image capture in addition to one or more of the above-described features. When in an image capture mode, the sensitivity of the signal processing circuitry is preferably increased, and the feature measurements can be stored in a volatile memory for read-out at a later time. Alternatively, the photosensitive sensor output signal can be digitized and directly routed to a volatile memory which stores the gray-scale image until it is read out at a later time. In either of these alternative embodiments, the image capture memory can be located in the same general physical location as the other optical reader circuitry, or else can be located external to the optical reader.
Further variations and modifications to the above are also described herein.